1. Field of the Invention
The present invention relates in general to fuel injection devices for a spark-ignition internal-combustion engine. More specifically, the invention provides an electronically controllable piezoelectric fuel injection device.
2. Description of the Prior Art
Japanese Patent Provisional Publication (Kokai) No. 60-164660A discloses a piezoelectric fuel injection valve integrally comprising a pump, a piezoelectric actuator for driving the pump, and an injection nozzle. In that piezoelectric fuel injection valve, the piezoelectric actuator is driven at a high frequency for fuel injection. Accordingly, it has response characteristics superior to those of a solenoid type fuel injection valve in Which the pump is driven by a solenoid actuator.
However, if this known piezoelectric fuel injection valve is to be used in a multicylinder engine, a separate and distinct piezoelectric . fuel injection valve must be provided for each cylinder. A fuel injection system including a plurality of such piezoelectric fuel injection valves is costly. Furthermore, the difference in operating characteristics among the various piezoelectric actuators causes irregular fuel distribution among the cylinders.
Japanese Patent Provisional Publication (Kokai) No. 61-108865 discloses a piezoelectric fuel injection device, which comprises a single pump and a single piezoelectric driving unit for driving the pump to distribute fuel pressurized by the pump to a plurality of injection nozzles respectively provided for a plurality of cylinders. The pump has only a single pump chamber connected to a plurality of injection nozzles by a plurality of pipes. Although only a single piezoelectric fuel injection device is used (as opposed to one for each cylinder), the difference in pipe flow characteristics among the various pipes causes irregular fuel distribution among the fuel injection nozzles.